The polycarbonate of 4,4'-isopropylidenediphenol (bisphenol A polycarbonate) is a well known engineering molding plastic. Bisphenol A polycarbonate is a clear high-performance plastic having good physical properties such as dimensional stability, high heat resistance, and good impact strength. Although bisphenol A polycarbonate has many good physical properties, its relatively high melt viscosity leads to poor melt processability and the polycarbonate exhibits poor chemical resistance.
Blends of the polycarbonates of bisphenol A and various dihydroxydiphenyl cycloalkanes have been used in making plastic films, molded articles, and extruded articles. These polycarbonate blends are especially useful in the performance plastics industry because they tend to have good heat resistance, high melt viscosities suitable for injection molding and extrusion, toughness, and good chemical resistance.
U.S. Pat. No. 5,034,457 discloses blends of dihydroxydiphenyl cycloalkane polycarbonates with a mixture of amorphous thermoplastics, partly crystalline thermoplastics, and rubber used for injection molding. U.S. Pat. No. 5,104,723 discloses blends of dihydroxydiphenyl cycloalkane polycarbonates with amorphous thermoplastics, partially crystalline thermoplastics, and elastomers for the production of films.
However, there has been no disclosure of miscible blends of dihydroxydiphenyl cycloalkane polycarbonates with other materials. Immiscible blend compositions are inadequate for many uses because they are opaque, and generally result in an unacceptable reduction in impact strength and tensile strength.
Clear, miscible blends of any two polymers are rare. The term "miscible" refers to blends that are a mixture on a molecular level wherein intimate polymer-polymer interaction is achieved. Miscible blends are clear, not translucent or opaque. In addition, differential scanning calorimetry testing detects only a single glass transition temperature (Tg) for miscible blends composed of two or more components.
There have been very few clear polycarbonate/polyester blends developed. U.S. Pats. No. 4,619,976 and 4,645,802 disclose clear blends based on bisphenol A polycarbonate with polyesters of poly(1,4-tetramethylene terephthalate), poly(1,4-cyclohexylenedimethylene terephthalate) and selected copolyesters and copoly(esterimides) of poly(1,4-cyclohexylenedimethylene terephthalate). U.S. Pat. No. 4,786,692 discloses clear blends of bisphenol A polycarbonate and polyesters of terephthalic acid, isophthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol. U.S. Pat. Nos. 4,188,314 and 4,391,954 disclose clear blends of bisphenol A polycarbonate with poly(1,4-cyclohexylenedimethylene terephthalate-co-isophthalate). These polyester blends do have improved chemical resistance and melt processability, when compared to unblended bisphenol A polycarbonate. However, the good heat resistance and impact strength of bisphenol A polycarbonate blends based on these compositions is reduced significantly.
In light of the above, it would be desirable to be able to form clear polyester blends of dihydroxydiphenyl cycloalkane polycarbonates having good melt processability suitable for injection molding. Such blend would be especially suitable for the manufacture of clear molded articles, fibers, sheeting, and film.